BEIJING — Websites of The Washington Post and the Guardian appear to now be blocked in China as the country’s government further tightens its so-called “Great Firewall” censorship apparatus as it navigates a politically sensitive period.

Until this weekend, The Post and the Guardian were among the last few major English-language outlets that were still regularly accessible from mainland China without the use of virtual private networking software, according to the censorship tracker Greatfire.org.

Chinese Internet authorities have gone into overdrive in recent weeks ahead of the 30th anniversary of the Tiananmen Massacre on June 4, 1989, prohibiting users on the popular WeChat social media service to post keywords or pictures related to the event.

All but the most oblique references to the incident were immediately scrubbed, and, during the days around the anniversary, users complained about not even being able to access the function to change their avatars.

Every language edition of Wikipedia was fully banned in mid-May. A CNN reporter said the network’s website was blocked again this week shortly after CNN.com ran a top story commemorating the 1989 event.

China’s Internet censors rarely, if ever, communicate their reasoning for blocking specific websites, and it’s not clear whether the ban would be permanent. Although authorities intermittently tighten and loosen their restrictions, the trend since 2013 has shown more and more foreign websites being irrevocably added to China’s blacklist.

Outlets such as Bloomberg, the New York Times, Reuters and the Wall Street Journal have been blocked for years. So have social media services such as Facebook and Twitter and all Google-owned services, including YouTube. Other popular services such as Dropbox, Slack and WhatsApp are also prohibited.

International business lobbies, media freedom groups and Western government officials — including U.S. trade negotiators — say the Great Firewall amounts to not only a restriction on speech but also fair practice.

The extensive censorship software now blocks more than 10,000 Web domains and is powered by artificial intelligence algorithms that tirelessly sharpen its ability to sniff out VPNs.

Chinese authorities have said their censorship practices are a matter of the country’s “Internet sovereignty” and not negotiable with foreign governments. But its officials have gone further in recent years, not only defending their approach to censorship but touting its successes as a model that authoritarian governments around the world could also adopt.

While a small number of Chinese users download VPNs to access banned websites and social media services, China has increasingly found ways to enforce the bans — including through physical intimidation.